1. Field of the Invention
This invention relates to a self-propelled material-processing apparatus.
2. Present State of the Art
It is known to provide self-propelled screening apparatus of the general type which comprise a chassis, a prime mover mounted on the chassis, moving means supporting the chassis and arranged to be power-operated by the prime mover in order to move the apparatus over the ground, a hopper arranged to receive a supply of bulk material to be screened by the apparatus, a conveyor arranged to receive material from the hopper and to convey such material to a discharge end of the conveyor, a screen arranged to receive material from the discharge end of the conveyor, and one or more discharge conveyors arranged to receive screened material from the screen and to discharge such material to a required deposition zone or zones, spaced outwardly of the chassis of the apparatus.
A self-propelled screening apparatus of the above general type may be used (a) to carry out screening operations on the move when it is required to form travelling deposits of screened material e.g. to fill-in a pipeline trench after laying of a pipeline, or to introduce hardcore or other foundation material to form the base of a road, or (b) to carry out static screening operations when required, but being capable of being moved from one position to another on a particular site when required.
A typical screening apparatus is of substantial overall length (when the component parts are deployed to screening and discharge positions), in that usually a hopper is arranged at one end of the chassis, a conveyor elevator extends lengthwise of the apparatus from the hopper to a discharge end above, or located outwardly of the opposite end of the chassis; and after material falls under gravity to the screen e.g. to a "screen box", and one (or more) discharge conveyor (which is arranged to receive screened material from the screen box) extends outwardly away from the chassis in order to deposit the screened material at a required deposition zone.
Discharge conveyors which may be used include so-called "tail conveyors", which discharge screened material rearwardly of the apparatus, and "side conveyors" which discharge the screened material laterally of the apparatus. Different discharge conveyors may be used to receive different screened "fractions" from the screen box, and to discharge such material to require deposition zones. A typical screening apparatus might have a single tail conveyor, and a pair of side conveyors, so that three different screened fractions or portions can be separated in the screen box, and discharged to separate discharge locations.
It is desirable for the apparatus to be easily manoeuvrable (in order to move from one static screening location to another, or to carry out screening operations "on the move"), and use of endless crawler tracks is therefore particularly suitable to form the moving means to propel, and to steer the apparatus. However, the length of a practical arrangement of endless tracks (to give required easy manoeuvrability) is much less than the overall length of the apparatus (when its component parts are deployed to screening/discharge positions), and in which they project outwardly of the chassis to substantial extents. This results in substantial inertial loads being generated when the apparatus is moving, and particularly when the apparatus is being steered. (This is somewhat similar to the inertial loads generated when an individual carries a horizontal ladder from a mid position and tries to rotate). It is therefore important to try, as far as possible, to maintain the overall centre of gravity of the apparatus (and its component parts) substantially centrally of the endless tracks, when in the deployed position.
In addition, endless track types of apparatus normally require to be transported on a "low loader", in order to move over the public highway from one site to another, and usually the component parts (and especially those which project from the chassis in the deployed position) must either be de-mounted, or else be moved to transport positions in which they at least reduce the extent of their projection from the chassis, before the apparatus can be transported on the low loader.
However, while the inertial loads of the deployed apparatus will be reduced, the much greater road speed of the low loader (compared with the self-propelled movement of a tracked apparatus in operation) means that any substantial mass of the apparatus (which is off-set from the centre of gravity of the apparatus) will apply substantial inertial load when the low loader goes around a bend of a road, or negotiates a roundabout.
This means that the apparatus must be very securely restrained when it is carried on a low loader, but even with such restraint, very substantial inertial loads generated when going round a bend in a road could still be very hazardous to other traffic, or may even result in the low loader being overturned e.g. if the low loader is towed around a roundabout at excessive speed.